DK173420B1

DK173420B1 - Liquid tank and centrifugal pump for discharging the liquid

Info

Publication number: DK173420B1
Authority: DK
Priority date: 1999-11-05
Filing date: 1999-11-05
Publication date: 2000-10-02
Also published as: DK199901599A

Description

DK 173420 B1 iDK 173420 B1 i

Opfindelsen vedrører en væsketank og centrifugalpumpe med i det væsentlige lodret pumpeaksel for udtømning af væsken, hvor pumpen er anbragt med sugesiden ved bunden af tanken og via en drivaksel forbundet med drivmidler for-5 trinsvist anbragt over"- tanken, hvor drivakselen med en kobling er i drivbar forbindelse med pumpens aksel, og hvor pumpen nær koblingen har et første hovedleje ved pumpeakselens øvre ende og et andet hovedleje modsat koblingen ved pumpeakselens nedre ende nær tankens bund, og 10 hvor der er forbindelse mellem tryksiden af pumpetrinet ud for hvert leje med det pågældende lejes lejeflader, og hvor der er afløb fra hvert leje til pumpetrinets sugeside .The invention relates to a liquid tank and centrifugal pump with substantially vertical pump shaft for discharging the liquid, the pump being arranged with the suction side at the bottom of the tank and via a drive shaft connected to propellants preferably disposed above the "tank where the drive shaft with a coupling is in drivable connection with the pump shaft, and where the pump near the coupling has a first main bearing at the upper end of the pump shaft and a second main bearing opposite the coupling at the lower end of the pump shaft near the bottom of the tank, and 10 where there is a connection between the pressure side of the pump stage next to each bearing thereof. the bearing surfaces of the bearing in question and where there is a drain from each bearing to the suction side of the pump stage.

Eksempler på væsketanke, hvor opfindelsen finder anven-15 delse, er tankene på et tankskib, men også andre typer af tanke, hvis indhold udtømmes ved hjælp af en pumpe anbragt ved tankens bund, er omfattede af opfindelsen. Tilførselen af smøremiddel, og det vil her sige pumpemedium, til hvert af pumpens hovedlejer sker gennem en kanal fra 20 tryksiden af det pumpetrin, der er ud for det pågældende leje, til lejets indvendige lejeflader. Hvert leje har da et afløb for smøremiddel til sugesiden af det tilsvarende pumpetrin. Så snart pumpen kører, og der er væske i tanken, vil der være tryk på smøremidlet til lejerne.Examples of liquid tanks in which the invention finds application are the tanks of a tanker, but also other types of tanks whose contents are discharged by means of a pump placed at the bottom of the tank are included in the invention. The supply of lubricant, that is to say pumping medium, to each of the main bearings of the pump takes place through a channel from the pressure side of the pumping step next to the bearing, to the inner bearing surfaces of the bearing. Each bearing then has a lubricant drain to the suction side of the corresponding pump stage. As soon as the pump is running and there is liquid in the tank, there will be pressure on the bearings lubricant.

25 Problemet med disse pumper opstår, hvis de får lov at køre, uden at der er væske i tanken, hvilket kan ske ved tømning af tanken, hvis ikke pumpen afbrydes, så snart tanken er tom. Når dette sker, vil især de dele af hovedlejerne, der optager de aksiale kræfter, udsættes for 30 kraftig opvarmning, hvilket fører til sammenbrud. Aksial-lejedelene bærer den samlede vægt af akselen med tilhørende skovlhjul, hvilket er en betydelige vægt, og dermed vil der udvikles en kraftig friktionsvarme, hvis lejerne ikke smørers tilstrækkeligt.25 The problem with these pumps arises if they are allowed to run without any liquid in the tank, which can happen when the tank is emptied if the pump is not shut down as soon as the tank is empty. When this occurs, especially those parts of the main bearings that absorb the axial forces will be subjected to excessive heating, leading to collapse. The axial bearing parts carry the total weight of the shaft with associated impeller, which is a considerable weight, and thus a strong frictional heat will be developed if the bearings are not sufficiently lubricated.

DK 173420 B1 2DK 173420 B1 2

For at afhjælpe dette problem er det første hovedleje nær koblingen ved pumpeakselens øvre ende et rent radialleje, og det andet hovedleje modsat koblingen ved pumpeakselens nedre ende er et radial- og aksialleje.To remedy this problem, the first main bearing near the coupling at the upper end of the pump shaft is a clean radial bearing, and the second main bearing opposite the coupling at the lower end of the pump shaft is a radial and axial bearing.

5 Da pumpen kun i ringe grad er selvansugende, vil der altid være en væskerest tilbage i tanken, som ikke pumpes op. Denne rest er imidlertid tilstrækkelig til, at det nederste hovedleje ved pumpens sugeside altid vil være helt eller delvist neddykket i væsken. Dermed sikr.es d^n 10 udvendige køling af dette leje.5 Since the pump is only slightly self-priming, there will always be a liquid residue left in the tank which is not pumped up. However, this residue is sufficient that the lower main bearing at the suction side of the pump will always be fully or partially submerged in the liquid. Thus, 10 external cooling of this bearing is ensured.

Desuden opsuges lejlighedsvis en vis mængde af væsken fra tankbunden i pumpen, f.eks. så meget at væskestanden ikke længere dækker indløbet, og herved vil der komme væsketryk i kanalen fra det første pumpetrins sugeside til det 15 nederste hovedlejes lejeflader, med det resultat at lejet smøres og køles. Når væskestanden ikke længere dækker indløbet til pumpen, vil væsken, der er suget op i pumpen, løbe tilbage til tanken, og en ny opsugning vil forekomme. Denne effekt sikrer nogen smøring og køling af 20 det nederste hovedleje, således at pumpens aksialleje sikres en vis køling og en vis smøring. Da samtidig det øverste leje er et rent radialleje, tåler det bedre at køre uden smøring og køling, da det på grund af den lodrette pumpeaksel ikke er tilsvarende højt belastet.In addition, a certain amount of the liquid from the tank bottom is occasionally absorbed into the pump, e.g. so much so that the liquid level no longer covers the inlet, and thereby the fluid pressure in the duct will come from the suction side of the first pump stage to the bearing surfaces of the bottom 15 main bearing, with the result that the bearing is lubricated and cooled. When the liquid level no longer covers the inlet of the pump, the liquid sucked up into the pump will return to the tank and a new suction will occur. This effect ensures some lubrication and cooling of the lower main bearing, so that the axial bearing of the pump ensures some cooling and some lubrication. Since at the same time the upper bearing is a clean radial bearing, it is better able to drive without lubrication and cooling, since it is not correspondingly high loaded due to the vertical pump shaft.

25 I en udførselsform for opfindelsen har hovedlejerne lejeflader af carbon eller siliciumkarbid. Carbonlejer tåler særdeles høje temperaturer, og desuden indeholder carbonlejer en vis mængde grafit, hvilket gør lejefladerne selvsmørende. Lejer med lejeflader af siliciumkarbid har 30 en lav friktion og samtidig en god varmeledningsevne, og dermed vil på den ene side friktionsvarmen ikke være overvældende, og den varme, der dannes, kan ledes bort ved varmeledning. Begge materialer tåler desuden urenhe- DK 173420 B1 3 der i smøremidlet, hvilket ofte vil forekomme, når der smøres med pumpemediet.In one embodiment of the invention, the main bearings have carbon or silicon carbide bearing surfaces. Carbon bearings can withstand extremely high temperatures, and carbon bearings also contain a certain amount of graphite, which makes the bearing surfaces self-lubricating. Bearings with silicon carbide bearing surfaces have a low friction and at the same time a good thermal conductivity, and on the one hand the frictional heat will not be overwhelming and the heat generated can be dissipated by heat conduction. In addition, both materials are resistant to impurities in the lubricant, which will often occur when lubricating with the pumping medium.

Særligt hensigtsmæssigt er det, hvis det øverste hovedleje har lejeflader i carbon, og det nederste har lejefla-5 der i siliciumkarbid. Herved udnyttes de to lejematerialers egenskaber bedst muligt, da det øvre leje har gavn af carbonmaterialets selvsmørende egenskaber og de varme-ledende egenskaber, og den lave friktion af siliciumkarbid lejet for neden sikrer lav varmeudvikling og god af-10 ledning af varmen.It is particularly convenient if the upper main bearing has carbon bearing surfaces and the lower one has bearing surfaces in silicon carbide. Hereby, the properties of the two bearing materials are best utilized as the upper bearing benefits from the self-lubricating properties of the carbon material and the heat-conducting properties, and the low friction of silicon carbide bedded below ensures low heat generation and good heat dissipation.

Tankskibe kan medføre mange typer medier f.eks. aggressive og giftige medier eller konsummedier. Drivakselen er omgivet af en kappe fyldt med olie eller tilsvarende smøremiddel for at smøre drivakselens lejer, og det må både 15 sikres, at dette smøremiddel ikke forurener tankindholdet, og at tankindholdet ikke trænger ind og forurener smøremidlet. Det er derfor fordelagtig, hvis koblingen mellem drivakselen og pumpeakselen er en magnetkobling, for derved at sikre fuldstændig adskillelse mellem de 20 oliesmurte og de pumpemedium smurte dele af konstruktionen.Tankers can carry many types of media eg. aggressive and toxic media or consumer media. The drive shaft is surrounded by a sheath filled with oil or equivalent lubricant to lubricate the bearings of the drive shaft, and it must be ensured both that this lubricant does not contaminate the tank contents and that the tank contents do not penetrate and contaminate the lubricant. Therefore, it is advantageous if the coupling between the drive shaft and the pump shaft is a magnetic coupling, thereby ensuring complete separation between the 20 oil-lubricated and the pump-medium lubricated parts of the structure.

Det er desuden et problem, at væsken i tanken ofte indeholder urenheder, der kan give slid på lejerne, og særligt hvis urenhederne indeholder magnetisk materiale som 25 f.eks. ikke oxideret jern i rustpartikler, vil disse aflej res på magnetkobl ingen, hvilket i værste fald kan betyde gennembrud af den membran, der adskiller de to sider af magnetkoblingen. Det er derfor hensigtsmæssigt, hvis der i forbindelsen mellem tryksiden af et pumpetrin og 30 det tilhørende hovedlejes lejeflader er et filter til udskillelse af urenheder og fortrinsvist et cyklonfilter.In addition, it is a problem that the liquid in the tank often contains impurities which can cause wear on the bearings, and especially if the impurities contain magnetic material such as e.g. non-oxidized iron in rust particles, these will be deposited on magnetic coupler none, which may at worst mean breakthrough of the membrane separating the two sides of the magnetic coupling. Therefore, it is convenient if there is a filter for separating impurities and preferably a cyclone filter in the connection between the pressure side of a pump stage and the bearing surfaces of the main bearing.

Herved sikres, at lejerne ikke udsættes for partikler, der kan give aflejringer og slid. Særligt for forbindel- DK 173420 B1 4 sen til det øvre hovedleje er dette vigtigt, da den væske, der tilføres her som smøremiddel, desuden smører og køler området mellem magnetkoblingens inderside og membranen, der adskiller olie-smurte og pumpemedium-smurte 5 dele. Et filter kan undværes ved det nederste hovedleje, særligt hvis dette udføres med en lejeflade i et hårdt materiale som siliciumkarbid.This ensures that the bearings are not exposed to particles that can cause deposits and wear. This is especially important for the connection to the upper main bearing, since the liquid supplied here as a lubricant additionally lubricates and cools the area between the inside of the magnetic coupling and the membrane separating oil-lubricated and pump-medium lubricated 5 parts. A filter can be avoided at the lower main bearing, especially if this is done with a bearing surface in a hard material such as silicon carbide.

Et særligt fordelagtigt filter er et cyklonfilter, da det ikke har filterdele, der skal udskiftes eller renses.A particularly advantageous filter is a cyclone filter as it does not have filter parts that need to be replaced or cleaned.

10 Restfraktionen fra cyklonfilteret føres tilbage i pumpen under det pumpetrin, hvorfra tilførslen sker.10 The residual fraction from the cyclone filter is returned to the pump during the pumping step from which the feed is made.

Opfindelsen vedrører desuden anvendelse af en væsketank og centrifugalpumpe ifølge krav 1 som en lagertank på et tankskib. Ved denne anvendelse opnås, at tømningen af la-15 gertanken bliver en særdeles driftsikker operation, og de pumpesammenbrud, der finder sted som følge af for sen afbrydelse af pumpen efter tømningen af tankskibes lagertanke, kan stort set undgås.The invention further relates to the use of a liquid tank and centrifugal pump according to claim 1 as a storage tank on a tanker. In this application, it is achieved that the emptying of the storage tank becomes a very reliable operation and the pump breakdowns which occur as a result of the late shutdown of the pump after the emptying of the tanker storage tanks can be largely avoided.

I det følgende skal et eksempel på opfindelsen gennemgås 20 i detaljer under henvisning til tegningen, hvor fig. 1 viser et sidebillede af en pumpe anbragt ved bunden af en tank, fig. 2 viser et delvist snitbillede af pumpen, fig. 3 viser et forstørret udsnit af området omkring det 25 øverste hovedleje og fig. 4 viser et forstørret udsnit af området omkring det nederste hovedleje.In the following, an example of the invention is described in detail with reference to the drawing, in which: FIG. 1 is a side view of a pump disposed at the bottom of a tank; FIG. 2 is a partial sectional view of the pump; FIG. 3 is an enlarged sectional view of the region of the top 25 main bearing and FIG. 4 shows an enlarged section of the area around the lower main bearing.

I fig. 1 ses et eksempel på en pumpe 1 anbragt i en væsketank, i dette tilfælde en lagertank i et tankskib, 30 hvor der over tanken på skibsdækket 2 er anbragt en motor DK 173420 B1 5 < (ikke vist), der via en aksel, fig. 2, nr. 6 står i driv bar forbindelse med pumpen 1. Akselen 6 er anbragt i et oliefyldt rør 3, der går fra motoren og ned til pumpen 1.In FIG. 1 shows an example of a pump 1 arranged in a liquid tank, in this case a storage tank in a tanker 30, where over the tank of the ship deck 2 is mounted a motor DK 173420 B1 5 (not shown) which via a shaft, fig. . 2, No. 6 is in operable connection with the pump 1. The shaft 6 is arranged in an oil-filled pipe 3 extending from the motor down to the pump 1.

Pumpen 1 har nederst et indløb 5 i afstand fra tankens 5 bund således, at væsken kan ledes frem til indløbet 5, og fra pumpen 1 er der et afgangsrør 4, der fører væsken op til dækshøjde. Som vist i fig. 1, er pumpen anbragt med indløbet 5 i en fordybning 31 i tankens bund, hvilket er med til at sikre en fuldstændig eller næsten fuldstændig 10 tømning af tanke.The pump 1 has at the bottom an inlet 5 at a distance from the bottom of the tank 5 so that the liquid can be led to the inlet 5, and from the pump 1 there is a discharge pipe 4 which carries the liquid up to the deck height. As shown in FIG. 1, the pump is arranged with the inlet 5 in a recess 31 in the bottom of the tank, which helps to ensure a complete or almost complete emptying of tanks.

I fig. 2 ses et delvist snit gennem pumpen 1, der er indrettet ifølge en udførelsesform for opfindelsen. Drlvåk-selen 6 i det oliefyldte rør 3 er fastholdt i forhold til pumpen l's pumpehus 7 af et kugleleje 8, og neden for 15 kuglelejet 8 er der til drivakselen 6 koblet et cylin drisk skørt 9, hvis indvendige side er belagt med permanentmagneter 10. Til pumpeakselen 11 er koblet et til det cylindriske skørt 9 modsvarende cylindrisk skørt 12, med permanentmagneter 10A på ydersiden. Mellem de to sæt per-20 manentmagneter 10 og 10A er der en klokkeformet membran 13, der for neden langs sin rand er hermetisk forbundet med pumpehuset 7's dæksel 14, og membranen 13 adskiller da de oliesmurte dele af konstruktionen fra de dele, der smøres med væsken i tanken, det vil her sige pumpens le-25 jer.In FIG. 2 shows a partial section through the pump 1 arranged according to an embodiment of the invention. The drillwave harness 6 in the oil-filled pipe 3 is held in relation to the pump housing 7 of the pump 1 by a ball bearing 8, and below the ball bearing 8 a cylindrical skirt 9 is connected to the drive shaft 6, the inside of which is coated with permanent magnets 10. To the pump shaft 11 is connected a cylindrical skirt 12 corresponding to the cylindrical skirt 9, with permanent magnets 10A on the outside. Between the two sets of permanent magnets 10 and 10A, there is a bell-shaped diaphragm 13 which is hermetically connected below the cover 14 of the pump housing 7, and the diaphragm 13 then separates the oil-lubricated parts of the structure from the parts lubricated with the liquid in the tank, that is, the pump bearings.

Pumpens første hovedleje 15 foroven er vist i stor målestok i fig. 3, og det andet hovedleje 16 forneden ses i stor målestok i fig. 4. Lejerne er glidelejer med hver sin indvendige lejering 15A og 16A fast monteret på akse-30 len 11, og hver to udvendige lejeringe 15B og 16B monteret fast i udvendige lejeringsholdere 15C og 16C hver i fast forbindelse med pumpehuset 7. De udvendige lejeringe 15B i det øvre hovedleje 15 optager kun radialkræfter, da der er indrettet en spalte 17 og 18 mellem lejeringene 6 DK 173420 B1 15B og de tilhørende aksialkraftoptagende lejeringe 19 og 20. De aksialkraftoptagene lejeringe 19 og 20 kan eventuelt undværes, men er bibeholdt i pumpen af sikkerhedshensyn.The first main bearing 15 of the pump 15 is shown on a large scale in FIG. 3, and the second main bearing 16 below is seen on a large scale in FIG. 4. The bearings are sliding bearings, each with their inner bearings 15A and 16A fixedly mounted on the shaft 11, and each two outer bearings 15B and 16B mounted firmly in the outer bearing holders 15C and 16C each in fixed connection with the pump housing 7. The outer bearings 15B in the upper main bearing 15, only radial forces are absorbed, since a gap 17 and 18 is arranged between the bearing rings 6 DK 173420 B1 15B and the associated axial force absorbing bearings 19 and 20. The axial force absorbing bearings 19 and 20 may be avoided, but are retained in the pump by safety.

5 I det nederste hovedleje sidder der aksialkraftoptagende lejeringe 21 og 22, der er fast forbundne med akselen 11, og har aksiale lejeflader vendende mod de to lejeringe 16B. De aksialkraftoptagende lejeringe 21 og 22 bærer pumpeakselens aksiale kræfter.5 In the lower main bearing there are axial force receiving bearings 21 and 22, which are firmly connected to the shaft 11, and having axial bearing faces facing the two bearings 16B. The axial force absorbing bearings 21 and 22 carry the axial forces of the pump shaft.

10 Fra tryksiden af det sidste pumpetrin er der et udtag 23 for pumpemedium til brug for smøring og køling af det øverste leje. Fra udtaget 23 er der over en filterindretning 24 en forbindelse 25, som via en kanal 26 i pumpehusets 7's dæksel leder pumpemediet under højt tryk ind i 15 området for lejet 15 og ind i området mellem membranen 13 og den indvendige side af magnetkoblingen. Yderligere kanaler 27 i dækselet og kanaler 28 i det sidste pumpetrins rotor danner afløb for smøremidlet til sugesiden af det sidste pumpetrin. Et system af kanaler sikrer smøremid-20 lets fordeling til de belastede flader, og dette er ikke nærmere angivet.10 From the pressure side of the last pump stage, there is a pump medium outlet 23 for lubrication and cooling of the upper bearing. From the outlet 23, over a filter device 24, there is a connection 25 which, via a duct 26 in the cover of the pump housing 7, carries the high pressure pump medium into the region of the bearing 15 and into the region between the diaphragm 13 and the inner side of the magnetic coupling. Additional channels 27 in the cover and channels 28 in the rotor of the last pump stage provide drainage for the lubricant to the suction side of the last pump stage. A system of ducts ensures distribution of the lubricant to the loaded surfaces, and this is not specified.

Da smøremidlet fra tanken kommer i kontakt med magnetkoblingen, er det yderst vigtigt, at der ikke i smøremidlet er magnetiske eller magnetiserbart materiale, da dette 25 vil aflejres på magneterne 10, 10A og føre til magnetkoblingens sammenbrud. Derfor er filterindretningen 24 yderst vigtig ved smøringen af det øverste leje, og en filterindretning, som er driftsikker, må vælges. I det aktuelle eksempel er valgt en cyklonseperator, der fjer-30 ner tunge partikler fra pumpemediet, og således sikkert fjerner mulig rust eller jernpartikler.As the lubricant from the tank comes into contact with the magnetic coupling, it is of the utmost importance that there is no magnetic or magnetizable material in the lubricant as this will deposit on the magnets 10, 10A and lead to the breakdown of the magnetic coupling. Therefore, the filter device 24 is extremely important in the lubrication of the top bearing and a filter device which is reliable must be selected. In the present example, a cyclone separator is selected which removes heavy particles from the pumping medium and thus safely removes possible rust or iron particles.

Det nederste hovedleje 16 smørers på tilsvarende måde. Et udtag 29 fra det første pumpetrins trykside er i væske- i DK 173420 B1 7 forbindelse med hovedlejet 16's lejeflader. Ved at vælge et stærkt lejemateriale bliver lejet her mindre følsomt over for forurening af smøremidlet, og dermed kan en filterindretning undværes, men det filter kan anvendes, hvis 5 behovet er der.The lower main bearing 16 is greased in a similar manner. An outlet 29 from the pressure side of the first pump stage is in liquid connection with the bearing surfaces of the main bearing 16. By choosing a strong bearing material, the bearing here becomes less sensitive to contamination of the lubricant, and thus a filter device can be avoided, but that filter can be used if the need is there.

Under drift smøres begge hovedlejer 15,16, så længe væskestanden i tanken når op over den rundtgående flange 30 omkring indløbet. Når væskestanden når under flangen 30's nederste rand, bryder pumpevirkningen af centrifugalpum-10 pen 1 sammen, og væsken i pumpen 1 og røret 4 løber tilbage og ned i tankens fordybning 31. Ved forsat drift af pumpen 1 vil smøringen af det øverste hovedleje 15 ophøre, men da dette er et radialleje, er det ikke særligt udsat, og hvis det ydermere har lejeflader af carbon, tå-15 ler det høje temperaturer, og som følge af den selvsmørende effekt sker der ikke sammenbrud af lejet før efter længere tids tørkørsel".In operation, both main bearings are lubricated 15,16 as long as the liquid level in the tank reaches above the circumferential flange 30 around the inlet. When the liquid level reaches below the lower edge of the flange 30, the pumping action of the centrifugal pump 1 breaks down, and the liquid in the pump 1 and the pipe 4 flows back and down in the recess 31 of the tank. Upon continued operation of the pump 1, the lubrication of the upper main bearing 15 will cease. but since this is a radial bearing, it is not particularly exposed and if it also has carbon bearing surfaces it can withstand high temperatures and due to the self-lubricating effect, the bearing does not collapse until after a long dry run " .

Væsken, der løber tilbage til fordybningen 31, vil undervejs passere udvendigt forbi det nederste hovedleje 16 og 20 afkøle lejet. Når væsken er løbet tilbage, vil væskestanden i fordybningen 31 stige, og evt. stige så meget, at pumpen 1 igen begynder at hæve væsken. Der kommer derved nogen smøring af det nederste leje 16, da udtaget 29 igen sættes under tryk. Det nederste hovedleje 16 smøres da 25 ved tørløb lejlighedsvist, og vil køles udvendigt. Denne effekt er tilstrækkelig til, at både radiale og aksiale lejeflader overlever i længere tid under tørkørsel. Særligt hvis lejet har lejeflader af siliciumkarbid, der har lav friktion og god varmeledningsevne, fås god holdbarhed 30 af lejet ved tørkørsel.______The liquid running back to recess 31 will pass along the exterior past the lower main bearing 16 and 20 to cool the bearing. When the liquid has run back, the liquid level in the recess 31 will rise, and possibly. increase so much that pump 1 again begins to raise the fluid. Thereby, there is some lubrication of the lower bearing 16, as the outlet 29 is again pressurized. The lower main bearing 16 is then lubricated 25 on dry occasions and will be cooled externally. This effect is sufficient for both radial and axial bearing surfaces to survive for a long time during dry driving. Especially if the bearing has silicon carbide bearing surfaces having low friction and good thermal conductivity, good durability of the bearing is obtained when drying .______

Claims

A washing tank and centrifugal pump (1) with substantially vertical pump shaft (11) for discharging the liquid, the pump (1) being arranged with the suction side (5) at the bottom of the tank and connected via a drive shaft (6) preferably disposed above the tank, where the drive shaft (6) with a coupling (10, 10A) is operably connected to the shaft (11) of the pump 10 (1) and the pump (1) near the coupling (10, 10A) has a first main bearing (15) at the upper end of the pump shaft (11) and a second main bearing (16) opposite the coupling (10, 10A) at the lower end of the pump shaft (11) near the bottom of the tank, and where there is a connection between the pressure side of the pump-petrine next to each bearing (15, 16) and the bearing surfaces of said bearing, and where there is a drain from each bearing to the suction side of the pump stage, characterized in that the first main bearing (15) near the coupling (10, 10A) at the upper end of the pump shaft (11) is a clean radial bearing (15) and the second main bearing (16) opposite the coupling (10, 10A) at the lower e of the pump shaft (11) nde is a radial and axial direction.

Liquid tank and centrifugal pump (1) according to claim 1, characterized in that the main bearings (15, 16) have 25 carbon or silicon carbide bearing surfaces.

Liquid tank and centrifugal pump (1) according to claim 1, characterized in that the coupling (10, 10A) between the drive shaft (6) and the pump shaft (11) is a magnetic coupling.

Liquid tank and centrifugal pump (1) according to claim 1, 30, characterized in that in the connection (25) between the pressure side of a pump stage and the bearing surfaces of the main bearing there is a filter (24) for separating impurities and preferably a cyclone filter. in DK 173420 B1.

Liquid tank and centrifugal pump (1) according to claim 4, characterized in that the residual fraction from the cyclone filter (24) is fed back into the pump for the pump step from which the withdrawal to the lubricant is made.

Use of liquid tank and centrifugal pump (1) according to claim 1 as storage tank on a tanker. 10